Where does the energy come from in a nuclear fission reaction
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Where does the energy come from in a nuclear fission reaction

[From: ] [author: ] [Date: 11-05-07] [Hit: ]
The equation e = mc^2 is supposed to indicatehow I can calculate the energy created from this fission reaction. What I dont understand is that among the two new atoms and the three neutrons, there is no loss of mass -- it all adds up to 236. So where is the mass from which I can calculate the energy released? Is it in fact the three neutrons? Or something else?......
A diagram in a chemistry book shows an atom of Uranium-235 being bombarded by a neutron. In the diagram this produces a U-236 atom which splits into a Barium-141 atom, a Krypton-92 atom, and three neutrons.
The equation e = mc^2 is supposed to indicate how I can calculate the energy created from this fission reaction. What I don't understand is that among the two new atoms and the three neutrons, there is no loss of mass -- it all adds up to 236. So where is the mass from which I can calculate the energy released? Is it in fact the three neutrons? Or something else?

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There is a loss of energy, and it's mass equivalent. In reality, energy is never lost, only changed from one form to another. It is better to say that energy is released. In any atom, the mass of the atom itself will be less that the sum of the masses of individual parts. This difference is called the "mass defect" and will be equivalent to the "binding energy".

When an atom undergoes fission, two or more fission fragments are formed along with the release of several neutrons. Each of these particles carry away some energy in the form of kinetic energy. But the big release of energy comes from the fact that the sum of the binding energies of the fission fragments is less than the binding energy of the original atom.

The difference in energy between the binding energy of U-235 and the sum of the binding energies of Ba-131 and Kr-192 is released as the energy you detect in a fission reaction. Since the binding energy has an equivalent mass, E=mc^2, then some small amount of mass is "lost" as the energy released in the fission process.

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First, the exact masses of the nuclei are not the same as the mass numbers in the equations. There are very slight variations in mass, but these variations are exceedingly important. In order to calculate the actual loss of mass, you would need the masses of the various nuclei and neutrons to several decimal places. Then, when you add up all the masses, you see that there is a very small change in the mass during the reaction. Since c^2 is such a huge number, even very small mass changes result in the release of a lot of energy.
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